?? TO_DATE格式?? Day:?? dd number 12?? dy abbreviated fri?? day spelled out friday?? ddspth spelled out, ordinal twelfth?? Month:?? mm number 03?? mon abbreviated mar?? month spelled out march?? Year:?? yy two digits 98?? yyyy four digits 1998??
2.?? select to_char( to_date(222,'J'),'Jsp') from dual??
显示Two Hundred Twenty-Two??
3.?? 求某天是星期几?? select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day') from dual;?? 星期一?? select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NLS_DATE_LANGUAGE = American') from dual;?? monday?? 设置日期语言?? ALTER SESSION SET NLS_DATE_LANGUAGE='AMERICAN';?? 也可以这样?? TO_DATE ('2002-08-26', 'YYYY-mm-dd', 'NLS_DATE_LANGUAGE = American')??
4.?? 两个日期间的天数?? select floor(sysdate - to_date('20020405','yyyymmdd')) from dual;??
5. 时间为null的用法?? select id, active_date from table1?? UNION?? select 1, TO_DATE(null) from dual;??
注意要用TO_DATE(null)??
6.?? a_date between to_date('20011201','yyyymmdd') and to_date('20011231','yyyymmdd')?? 那么12月31号中午12点之后和12月1号的12点之前是不包含在这个范围之内的。?? 所以，当时间需要精确的时候，觉得to_char还是必要的?? 7. 日期格式冲突问题?? 输入的格式要看你安装的ORACLE字符集的类型, 比如: US7ASCII, date格式的类型就是: '01-Jan-01'?? alter system set NLS_DATE_LANGUAGE = American?? alter session set NLS_DATE_LANGUAGE = American?? 或者在to_date中写?? select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NLS_DATE_LANGUAGE = American') from dual;?? 注意我这只是举了NLS_DATE_LANGUAGE，当然还有很多，?? 可查看?? select * from nls_session_parameters?? select * from V$NLS_PARAMETERS??
8.?? select count(*)?? from ( select rownum-1 rnum?? from all_objects?? where rownum <= to_date('2002-02-28','yyyy-mm-dd') - to_date('2002-?? 02-01','yyyy-mm-dd')+1?? )?? where to_char( to_date('2002-02-01','yyyy-mm-dd')+rnum-1, 'D' )?? not?? in ( '1', '7' )??
Monday-Sunday, for format code DAY?? Mon-Sun, for format code DY?? 1-7, for format code D??
11?? select to_char(sysdate,'hh:mi:ss') TIME from all_objects?? 注意：第一条记录的TIME 与最后一行是一样的?? 可以建立一个函数来处理这个问题?? create or replace function sys_date return date is?? begin?? return sysdate;?? end;??
select to_char(sys_date,'hh:mi:ss') from all_objects;?? 12.?? 获得小时数??
SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 2:38:40') from offer?? SQL> select sysdate ,to_char(sysdate,'hh') from dual;??
